Display panel, method for preparing the same, and display device

ABSTRACT

The present disclosure relates to a display panel, a method for preparing the same and a display device. The display panel includes a first electrode, a light emitting structure, a second electrode and a scattering layer stacked in sequence. The second electrode is a transparent electrode. One side of the scattering layer away from the second electrode is configured as a light emergent side. The surface of the one side of the scattering layer away from the second electrode is a rough surface, and the RMS of the roughness of the rough surface ranges from 50 nm to 200 nm.

The present application claims priority to Chinese Patent ApplicationNo. 201911011581.8 filed with the Chinese Patent Office on Oct. 23,2019, which is hereby incorporated by reference in its entirety.

FIELD

The present disclosure relates to the technical field of display, inparticular to a display panel, a method for preparing the display panel,and a display device.

BACKGROUND

Serving as a novel light emitting material, a Quantum Dot (QD) has theadvantages such as high color purity of light, high light emittingquantum efficiency, light emitting color adjustability and long servicelife so as to become a current research hotspot of a novel LED lightemitting material. Therefore, a Quantum dot Light Emitting Diode (QLED)with a quantum dot material as a light emitting layer has become a mainresearch direction of a novel display device at present.

SUMMARY

The present disclosure discloses a display panel, a method for preparingthe display panel, and a display device.

The display panel includes a first electrode, a light emittingstructure, a second electrode and a scattering layer stacked insequence. The second electrode is a transparent electrode. One side ofthe scattering layer away from the second electrode is configured as alight emergent side. The surface of the one side of the scattering layeraway from the second electrode is a rough surface, and the RMS of theroughness of the rough surface ranges from 50 nm to 200 nm.

The display device includes the above-mentioned display panel.

The method for preparing a display panel includes respectively preparinga first electrode, a light emitting structure, a second electrode and ascattering layer. The first electrode, the light emitting structure, thesecond electrode and the scattering layer are stacked in sequence. Thesecond electrode is a transparent electrode. One side of the scatteringlayer away from the second electrode is configured as a light emergentside. The surface of the one side of the scattering layer away from thesecond electrode is a rough surface, and the RMS of the roughness of therough surface ranges from 50 nm to 200 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a sectional structure of a displaypanel provided by an embodiment of the present disclosure;

FIG. 2 is a schematic diagram of emergent light paths of rays passingthrough a scattering layer in two cases that the surface of thescattering layer is smooth and the surface of the scattering layer isrough;

FIG. 3 is a schematic diagram of a sectional structure of a displaypanel provided by an embodiment of the present disclosure;

FIG. 4 is a schematic diagram of a sectional structure of a displaypanel provided by an embodiment of the present disclosure;

FIG. 5 is a schematic diagram of a sectional structure of a displaypanel provided by an embodiment of the present disclosure;

FIG. 6 is a schematic diagram of a sectional structure of a displaypanel provided by an embodiment of the present disclosure; and

FIG. 7 is a schematic diagram of a scattering layer provided by anembodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The technical solutions in the embodiments of the present disclosurewill be clearly and completely described below in combination with theaccompanying drawings in the embodiments of the present disclosure.Obviously, the described embodiments are not only a part of theembodiments of the present disclosure, but not all the embodiments.Based on the embodiments in the present disclosure, all otherembodiments obtained by those of ordinary skill in the art withoutcreative work shall fall within the protection scope of the presentdisclosure.

In the related art, for a QLED display product, a light emitting layercommonly adopts a top emission structure due to the demand of highresolution. In the top emission structure, a top electrode generallyadopts a semitransparent electrode such as a thin film made of a metalsuch as Al and Ag. On one hand, the transmissivity of a thin film ofthin metal is relatively low to affect the light emergent efficiency ofthe device; and on the other hand, a microcavity effect also makes thecontrol of light extraction efficiency become very complex and is notbeneficial to the improvement on light emergent efficiency.

As shown in FIG. 1, and FIG. 3 to FIG. 6, an embodiment of the presentdisclosure provides a display panel including a first electrode 2, alight emitting structure 3, a second electrode 4 and a scattering layer5 stacked in sequence. The second electrode 4 is a transparentelectrode. One side of the scattering layer 5 away from the secondelectrode 4 is configured as a light emergent side. The surface of theone side of the scattering layer 5 away from the second electrode 4 is arough surface, and the RMS of the roughness of the rough surface rangesfrom 50 nm to 200 nm. Optionally, the transparent electrode refers to anelectrode prepared by a transparent conductive oxide material such asindium tin oxide (ITO), indium zinc oxide (IZO) and fluorine-doped tinoxide (FTO).

In the above-mentioned display panel, the second electrode 4 is locatedat one side of the light emitting structure 3 away from a substrate 1and is used as an electrode at the light emergent side. The secondelectrode 4 is made of a transparent electrode material so as to havehigher transmissivity and light emergent efficiency than an electrodematerial made of a metal such as Al and Ag. Moreover, the light emergentside of the second electrode 4 is further provided with the scatteringlayer 5. The surface of the scattering layer 5 is a rough surface, andthe Root-Mean-Square (RMS) value of the roughness of the rough surfaceranges from 50 nm to 200 nm, so that rays may be scattered, andfurthermore, the light emergent efficiency of the display panel iseffectively increased. Based on the above, the above-mentioned displaypanel is relatively high in light emergent efficiency and relativelygood in display effect.

The surface of the scattering layer 5 is a rough surface. Known bycomparing two scattering layers 5, i.e., (a) and (b) in FIG. 2, therough surface of the scattering layer 5 may avoid total reflection ofthe rays on the surface and increase the light emergent rate of the raysand meanwhile may also improve the refraction effect of the rays on thesurface of the scattering layer 5, enhance the converging effect of therays in an emergent process and increase the front light emergent rate.

Optionally, the display panel provided by the embodiment of the presentdisclosure may be a top emission device or a bottom emission device.Specifically, the display panel includes the substrate 1, if the displaypanel is the top emission device, as shown in FIG. 1, FIG. 3 and FIG. 4,the substrate 1 is arranged close to the first electrode 2; and if thedisplay panel is the bottom emission device, as shown in FIG. 5 and FIG.6, the substrate 1 is arranged close to the scattering layer 5.

In an embodiment, the refractive index of the scattering layer 5 isgreater than that of the second electrode 4.

In the related art, take the top emission device as an example, therefractive index of a top semitransparent cathode (a thin film made of ametal such as Al and Ag) is greater than that of air, and the rays areeasy to reflect on the cathode so that parts of the rays may not beemitted from the cathode. In the embodiment of the present disclosure,the scattering layer 5 with the higher refractive index is provided onthe surface of the second electrode 4, so that the phenomenon that therays may not be emitted due to total reflection of the rays on aninterface of the second electrode 4 and the scattering layer 5 may beprevented, and therefore, the emitting efficiency may be furtherincreased.

Exemplarily, the second electrode 4 is a transparent electrode and ismade of a material such as indium tin oxide (ITO) and indium zinc oxide(IZO) with the refractive index being about 1.7 to 1.9.

Exemplarily, the refractive index of the material of the scatteringlayer 5 may be 2 to 2.5.

Exemplarily, the material of the scattering layer may include aninorganic material such as oxides and nitrides and may also include anorganic material such as a macromolecular polymer. For example, thescattering layer 5 may be made of an inorganic insulating material suchas SiN_(x), SiON_(x), TiO_(x), ZrO_(x) and HfO_(x) and may also be madeof an organic material such as PMMA.

In some embodiments, as shown in FIG. 1, and FIG. 3 to FIG. 6, thescattering layer 5 is of patterned array structures; the display panelfurther includes a third electrode 6 (the shaded parts shown in FIG. 1,FIG. 3, and FIG. 4 to FIG. 6) located at one side of the scatteringlayer 5 away from the second electrode 4; and the third electrode 6 isconnected with the second electrode 4 through a gap among the arraystructures, and the third electrode 6 and the second electrode 4 jointlyform an electrode structure at the light emergent side of the displaypanel so that the resistance of the electrode at the light emergent sidemay be effectively reduced, and the performance of a light emittingdevice may be improved.

In some implementations, the work function of the third electrode 6 isgreater than that of the second electrode 4, and the lighttransmissivity of the third electrode 6 is greater than that of thesecond electrode 4.

Exemplarily, as shown in FIG. 3 and FIG. 5, the first electrode 2 isconfigured as an anode, and the second electrode 4 and the thirdelectrode 6 are configured as cathodes; and the light emitting structure3 includes a hole injection layer (HI) 31, a hole transport layer (HT)32, a quantum dot light emitting layer (QD) 33 and an electron transportlayer (ET) 34 sequentially arranged in a direction from the firstelectrode 2 to the second electrode 4. Optionally, as shown in FIG. 3and FIG. 5, the second electrode 4 is in contact with the electrontransport layer 34, and the work function of the second electrode 4 ismatched with the energy level of the electron transport layer 34.

The work function of the second electrode is matched with the energylevel of the electron transport layer, which may be understood as thatthe work function of the second electrode is approach to a numericalvalue of the HOMO energy level of the electron transport layer, and adifference value thereof is generally not greater than 0.3 eV, forexample, the difference value of the work function of the secondelectrode and the HOMO energy level of the electron transport layer maybe 0 eV, 0.1 eV, 0.2 eV or 0.3 eV.

Exemplarily, the hole injection layer 31 may be made of an organicinjection material such as PEDOT:PSS or an inorganic oxide such as MoOx.The hole transport layer 32 may be made of an organic transport materialsuch as PVK, TFB and TPD or an inorganic oxide such as NiOx and VOx. Theelectron transport layer 34 may select ZnO nanoparticles or Mg-doped ZnOnanoparticles. Exemplarily, the second electrode 4 and the thirdelectrode 6 are made of the same material and may be ahigh-transmissivity electrode prepared by adopting a magnetronsputtering process. Optionally, the second electrode 4 and the thirdelectrode 6 are made of an indium zinc oxide (IZO) material. In apreparation process, the indium zinc oxide (IZO) electrode is directlydeposited to be formed by adopting a magnetron sputtering way withoutundergoing an annealing process, so that influences on an electrodelayer on a lower layer may be avoided.

Exemplarily, the work function of the second electrode 4 is relativelylow, is about 4.2 eV-4.4 eV and is approach to the energy level of aconduction band of the electron transport layer 34, an electroninjection barrier is relatively proper, but the transmissivity of thesecond electrode is relatively low and is about 40%; and the thirdelectrode 6 may achieve high transmissivity of 90% or above by adoptingan oxygen doping process and has the work function of about 5.6 eV.Specifically, in an embodiment of the present disclosure, the cathodestructurally includes two layers including the third electrode 6 and thesecond electrode 4, so that the resistance of the cathode may beeffectively reduced, and the performance of the light emitting devicemay be improved. Meanwhile, the second electrode 4 is in contact withthe electron transport layer 34, and the energy level of the secondelectrode 4 is matched with that of the electron transport layer 34 sothat the performance of the light emitting device may be furtherguaranteed. In addition, the second electrode 4 may select a process inwhich no oxygen is doped in an IZO sputtering process according to arequirement that the work function of the second electrode 4 is matchedwith the energy level of the electron transport layer 34 (such as a ZnOlayer), then the transmissivity of the second electrode 4 prepared isrelatively low, while the third electrode 6 is away from the electrontransport layer 34, so that an oxygen-doping sputtering process by whichhigh transmissivity may be realized may be selected, and thetransmissivity is relatively high; and in the embodiment of the presentdisclosure, through the two-layer structure of the third electrode 6 andthe second electrode 4, not only may the performance of the lightemitting device be guaranteed, but also the transmissivity of theelectrode structure at the overall light emergent side may be increased.

Exemplarily, as shown in FIG. 3 and FIG. 5, the thickness of the thirdelectrode 6 is greater than that of the second electrode 4.

In the embodiments of the present disclosure, the thickness of the thirdelectrode 6 with relatively high transmissivity is greater than that ofthe second electrode 4 with relatively low transmissivity, so that thetransmissivity of the electrode structure at the overall light emergentside may be further increased under the condition that the performanceof the light emitting device is guaranteed.

Exemplarily, the thickness of the second electrode 4 may be 10 nm-100nm. The thickness of the third electrode 6 is greater than 100 nm andmay be specifically determined according to an actual demand.

In another optional implementation, as shown in FIG. 4 and FIG. 6, thefirst electrode 2 is configured as a cathode, and the second electrode 4is configured as an anode; the light emitting structure 3 includes anelectron transport layer 34, a quantum dot light emitting layer 33, ahole transport layer 32 and a hole injection layer 31 sequentiallyarranged in a direction from the first electrode 2 to the secondelectrode 4; the second electrode 4 is in contact with the holeinjection layer 31, and the work function of the second electrode 4 ismatched with the energy level of the hole injection layer 31, namely thework function of the second electrode 4 is approach to a numerical valueof the HOMO energy level of the hole injection layer 31, and adifference value thereof is generally not greater than 0.3 eV, forexample, the difference value of the work function of the secondelectrode and the HOMO energy level of the hole injection layer may be 0eV, 0.1 eV, 0.2 eV or 0.3 eV. Optionally, the second electrode 4 may bemade of an indium zinc oxide (IZO) material, the work function of thesecond electrode 4 is approach to the HOMO energy level of the holeinjection layer 31 and is a greater numerical value, and hightransmissivity of 90% or above may be achieved by adopting anoxygen-doping sputtering process. In this condition, the thickness ofthe second electrode 4 may be set to be greater to improve theperformance of the anode, meanwhile, the brightness of emergent lightmay not be greatly affected, and furthermore, in some embodiments, thethird electrode may be omitted.

In some embodiments, the scattering layer 5 is of a structure ofphotonic crystals, filtration and light extraction may be realizedthrough the scattering layer 5, then the light emergent efficiency andfront light emergent efficiency of the display panel may be furtherincreased.

A structure of photonic crystals refers to an artificial periodicdielectric structure with a photonic band-gap (PBG for short)characteristic, in other words, the structure of photonic crystals is ofa periodic array structure, and the dimension in each period is thelattice dimension of the photonic crystal and determines the filteredand extracted light wavelength.

Exemplarily, the display panel includes sub-pixels with differentcolors, and the lattice dimension of the photonic crystal of thescattering layer 5 and the wavelength of light correspondingly output byeach sub-pixel are within the same dimension magnitude range and areboth nanoscale. Specifically, the display panel includes a red pixel, agreen pixel and a blue pixel, and lattice dimensions of photoniccrystals in the red pixel, the green pixel and the blue pixelrespectively range from 150 nm to 200 nm, from 250 nm to 300 nm and from350 nm to 400 nm.

Exemplarily, as shown in FIG. 7, the thickness of the scattering layer 5(the thickness of the photonic crystal) may be 50 nm-500 nm.

Of course, as shown in FIG. 7, the array structures of the scatteringlayer 5 may also adopt array patterns with randomly distributed shapesand dimensions, rather than the periodic photonic crystal structures.

In addition, exemplarily, in the embodiments of the present disclosure,the substrate 1 may be a glass or flexible PET substrate, and the firstelectrode 2 may be a transparent electrode made of an indium tin oxide(ITO), a fluorine-doped tin oxide (FTO) or a conductive polymer or anon-transparent electrode made of a metal such as Al and Ag, which maybe specifically determined according to an actual demand.

Moreover, an embodiment of the present disclosure further provides adisplay device which may include any one of the above-mentioned displaypanel.

Optionally, the display device in the embodiment of the presentdisclosure may be a top emission quantum dot light emitting diodedisplay device (QLED) and may be specifically used for a television, adisplay, a notebook computer and a tablet personal computer.

Based on the display panel provided by the embodiments of the presentdisclosure, the present disclosure further provides a method forpreparing the display panel.

The method for preparing the display panel includes respectivelypreparing a first electrode, a light emitting structure, a secondelectrode and a scattering layer. The first electrode, the lightemitting structure, the second electrode and the scattering layer arestacked in sequence. The second electrode is a transparent electrode.One side of the scattering layer away from the second electrode isconfigured as a light emergent side. The surface of the one side of thescattering layer away from the second electrode is a rough surface, andthe RMS of the roughness of the rough surface is 50 nm-200 nm.

Optionally, the operation of preparing the scattering layer include:

depositing a scattering layer material; and

roughening a surface of one side of the scattering layer material awayfrom the second electrode by using a plasma etching process or a sandblasting process to make the RMS of the roughness of the surface be 50nm-200 nm.

In some embodiments, the method further include:

forming patterned array structures for the scattering layer by using apatterning process; and

forming a third electrode on the scattering layer, wherein the thirdelectrode is connected with the second electrode through a gap among thepatterned array structures, the work function of the third electrode isgreater than that of the second electrode, and the light transmissivityof the third electrode is greater than that of the second electrode.

In some embodiments, the operations of preparing the scattering layerand forming the patterned array structures for the scattering layer byusing the patterning process may include: depositing an oxide materiallayer or a nitride material layer by adopting a PECVD process, andforming the patterned array structures by using a photolithographicprocess (including operations such as photoresist coating, developing,etching and stripping).

In some embodiments, the operations of preparing the scattering layerand forming the patterned array structures for the scattering layer byusing the patterning process may include: preparing a PMMA materiallayer by adopting a wet film forming process, and forming the patternedarray structures by using a nano-imprinting process.

In some embodiments, the second electrode and the third electrode may berespectively deposited in a way of sputtering the IZO.

Exemplarily, the operation of forming the light emitting structure mayinclude: sequentially preparing a hole injection layer (HI), a holetransport layer (HT), a quantum dot light emitting layer (QD) and anelectron transport layer (ET).

Exemplarily, the method for preparing the display panel provided by thepresent disclosure may further include operations such as forming apixel defining layer and forming a packaging layer, the descriptionsthereof are omitted herein.

Obviously, the skilled in the art can make various alterations andvariations on the embodiments of the present disclosure withoutdeparting from the spirit and scope of the present disclosure. In thisway, if the alterations and variations of the present disclosure fallwithin the scopes of the claims of the present disclosure and theirequivalent technologies, the present disclosure is also intended toinclude the alterations and variations.

What is claimed is:
 1. A display panel, comprising a first electrode, alight emitting structure, a second electrode and a scattering layerstacked in sequence; wherein, the second electrode is a transparentelectrode; one side of the scattering layer away from the secondelectrode is configured as a light emergent side; a surface of the oneside of the scattering layer away from the second electrode is a roughsurface, and a Root-Mean-Square (RMS) value of roughness of the roughsurface ranges from 50 nm to 200 nm; and a refractive index of thescattering layer is greater than that of the second electrode.
 2. Thedisplay panel according to claim 1, wherein the scattering layer is ofpatterned array structures; and the display panel further comprises: athird electrode located at the one side of the scattering layer awayfrom the second electrode; wherein, the third electrode is connectedwith the second electrode through a gap among the patterned arraystructures; a work function of the third electrode is greater than thatof the second electrode; and a light transmissivity of the thirdelectrode is greater than that of the second electrode.
 3. The displaypanel according to claim 2, wherein: the first electrode is configuredas an anode, and the second electrode and the third electrode areconfigured as cathodes; the light emitting structure comprises a holeinjection layer, a hole transport layer, a quantum dot light emittinglayer and an electron transport layer sequentially arranged in adirection from the first electrode to the second electrode; and thesecond electrode is in contact with the electron transport layer, andthe work function of the second electrode is matched with an energylevel of the electron transport layer.
 4. The display panel according toclaim 2, wherein the second electrode and the third electrode are madeof the same material.
 5. The display panel according to claim 4, whereinthe second electrode and the third electrode are made of an indium zincoxide material.
 6. The display panel according to claim 2, wherein athickness of the third electrode is greater than that of the secondelectrode.
 7. The display panel according to claim 6, wherein thethickness of the second electrode ranges from 10 nm to 100 nm.
 8. Thedisplay panel according to claim 1, wherein, the first electrode isconfigured as a cathode, and the second electrode is configured as ananode; the light emitting structure comprises an electron transportlayer, a quantum dot light emitting layer, a hole transport layer and ahole injection layer sequentially arranged in a direction from the firstelectrode to the second electrode; and the second electrode is incontact with the hole injection layer, and a work function of the secondelectrode is matched with an energy level of the hole injection layer.9. The display panel according to claim 1, wherein, the scattering layeris of a structure of photonic crystals; and the display panel comprisesa red pixel, a green pixel and a blue pixel, and lattice dimensions ofphotonic crystals in the red pixel, the green pixel and the blue pixelrespectively range from 150 nm to 200 nm, from 250 nm to 300 nm and from350 nm to 400 nm.
 10. The display panel according to claim 1, wherein amaterial of the scattering layer comprises at least one of: oxides,nitrides and macromolecular polymers.
 11. The display panel according toclaim 10, wherein the material of the scattering layer comprises atleast one of: SiN_(x), SiON_(x), TiO_(x), ZrO_(x), HfO_(x) andPolymethyl Methacrylate (PMMA).
 12. A display device, comprising thedisplay panel according to claim
 1. 13. A method for preparing a displaypanel according to claim 1, comprising: respectively preparing the firstelectrode, the light emitting structure, the second electrode and thescattering layer; wherein, the first electrode, the light emittingstructure, the second electrode and the scattering layer are stacked insequence; the second electrode is a transparent electrode; one side ofthe scattering layer away from the second electrode is configured as alight emergent side; a surface of the one side of the scattering layeraway from the second electrode is a rough surface, and aRoot-Mean-Square (RMS) value of roughness of the rough surface rangesfrom 50 nm to 200 nm; and a refractive index of the scattering layer isgreater than that of the second electrode.
 14. The method according toclaim 13, wherein the preparing the scattering layer comprises:depositing a scattering layer material; and roughening a surface of oneside of the scattering layer material away from the second electrode byusing a plasma etching process or a sand blasting process to make theRMS of the roughness of the surface range from 50 nm to 200 nm.
 15. Themethod according to claim 13, further comprising: forming patternedarray structures for the scattering layer by using a patterning process;and forming a third electrode on the scattering layer, wherein the thirdelectrode is connected with the second electrode through a gap among thepatterned array structures, a work function of the third electrode isgreater than that of the second electrode, and a light transmissivity ofthe third electrode is greater than that of the second electrode. 16.The method according to claim 15, wherein the preparing the scatteringlayer and the forming the patterned array structures for the scatteringlayer by using the patterning process comprise: depositing an oxidematerial layer or a nitride material layer by adopting a Plasma EnhancedChemical Vapor Deposition (PECVD) process, and forming the patternedarray structures by using a photolithographic process; or preparing aPolymethyl Methacrylate (PMMA) material layer by adopting a wet filmforming process, and forming the patterned array structures by using anano-imprinting process.